Aeroplane fabric



Patented Dec. 19, 1933 1,94o,212 AEROPLANE memo Guy 0. Given, Parlin, Harold W. Letts, South River, and Norman W. Thomson, Parlin,

N. J., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of 7 Delaware No Drawing. Application May 21, 1929 Serial No. 364,938

Claims.

This invention relates to the art of coating compositions, and more particularly to compositions for use in coating aeroplane and similar fabrics.

Various compositions have heretofore been pro- 5 posed as dopes for the treatment of aeroplane and similar fabrics in order to give the special properties required, the most unusual of which is that of exerting a permanent shrinking or tautening effect on the fabric. In addition these finishes should exhibit the maximum degree of durability and hence must be flexible, unaffected by temperature changes, and impervious to the action of water, air, gasoline or oil; light in weight; and capable of producing a finish showing good build and luster when produced in a variety of colors. As heretofore practiced it has been customary to apply a cellulose nitrate lacquer over the undercoat dope to secure some degree of durability and to produce color effects but, so far as known to us, however, it has not been possible heretofore to secure the desired build and lusterwithout'sacrificing durability of the coating system.

If lacquers are applied over a cellulose nitrate dope, the solvent softener, carried by the solvents in the lacquer, penetrates the nitrate undercoat, thus softening the latter unduly and absorbing some of the needed softener from the top coat. This causes the treated fabric to have insufficient flexibility and a loss of tautness, and the sinking caused by the penetration of the undercoat interferes with the build and luster, and renders additional applications necessary in order to attain these desired effects, resulting in an objection- .terial required.

On the other hand, if lacquers are applied over a cellulose acetate dope, the penetration of the undercoats by the solvents is avoided, but there is an insufficient bond between the lacquer and the undercoats which permits the former to flake ofi,-the dope is less moisture resistant, lacks the desired durability, and costs materially more.

,Again, if the solvent softener is omitted from the lacquer or materially reduced therein, in order to avoid penetration of the dope, the re-' sulting finish is not sufliciently flexible and will soon' fail by checking because all low viscosity able increase in weight as well as in time and ma-- cellulose nitrate solutions must have a solvent iolfttener present in order to have sufiicient dura- We have found that the desired combination of durability, build and luster can be obtained by using a dope which comprises a mixture of cellulose esters, one of which is soluble in the solvents of the pigmented lacquer to be applied thereover, a common solvent softener for the cellulose esters, and a common volatile solvent mixture for the cellulose esters and softener.

It is therefore an object of our invention to provide a new aeroplane dope which will give satisfactory results when applied under a pigmented lacquer.

It is another object of our invention to provide a coatingsystem for aeroplane and similar fabrics which will give high build and luster combined with satisfactory durability.

It is a further object of our invention to provide a new method of coating aeroplane and similar fabrics.

With the above and other objects in view, which will be apparent as the description proceeds, we have set forth our invention in this specification and illustrated it by the following typical'embodiments which are given by way of illustration and not as a limitation.

EXAMPLE 1 Aeroplane dope EXAMPLE 2 Lacquer Parts by weight Pyroxylin (low viscosity, e. g. that of Flaherty 1,629,999) 10 Dibutyl phthalate 5 Linseed oil 15 Chrome yellow 20 Damar 3 Solvent (butyl acetate 20, ethyl alcohol 5,

ethyl acetate 10, and toluene 12) 47 In the preferred embodiment of our invention the fabric to be treated, which may be of any suitable weave or material, such as cotton or linen, is stretched as tightly as possible over the framework of the aeroplane or other article, and it is then given a plurality of clear undercoats, for instance of the dope set forth in Example 1, allowing from hour to 1 hour for air drying between the application of successive coats. It is then given a plurality of coats of flexible enamel, such as that set forth in Example 2, allowing 1 hour between successive coats for air drying.

If desired, the dry undercoat system may be sanded, but for most purposes this has been found to be unnecessary when a dope of the type set forth herein is utilized.

In the preferred embodiment of our invention we use 4 clear undercoats and 2 coats of flexible enamel, the undercoats being preferably applied by brushing and the flexible enamel by spraying, but we do not wish to limit ourselves to the specific number of coats, to the specific drying periods or to the method of applying the coats, except as indicated by the following claims.

Likewise, we do not wish to be limited to the specific compositions set forth above, as the essential ingredients of our dope are merely a mixture of cellulose esters, one of which is soluble in the solvents of a subsequently applied lacquer coat, a common solvent softener for these esters, and a volatile solvent mixture capable of dissolving each of the other ingredients.

For example, the cellulose acetate-pyroxylin ratio may be varied from a :10 ratio to a 25:75 ratio. The tricresyl phosphate may be replaced by other materials which similarly function as common solvent softeners for the cellulose esters, such as triphenyl phosphate, dimethyl phthalate, dibutyl tartrate, and triacetin, al-.

though we have obtained the best results with tricresyl phosphate. Similarly, while we have found 3% of tricresyl phosphate to be the maxi mum amount for obtaining te best results, this may be varied from l/30 to of the weight of the cellulose esters used. The solvent mixture may also be varied considerably. For example, the benzol may be entirely replaced by other ingredients, such as methyl alcohol. Similarly, the diacetone alcohol and ethyl lactate can, if desired, be replaced by the monomethyl ether of ethylene glycol. L

Similarly, the composition of the lacquer may be varied over wide limits, for examples as disclosed in Hitt Patent, 1,710,453, Example 3. We prefer, however, a pyroxylin enamel containing a ratio of pyroxylin to plasticizer of 10:20 and the use of only a small percentage. of resin, and in general we prefer to maintain the following general ratios:

Parts by The quantity of solvent, as well as its components, may be varied considerably in the manner well known in the art, to produce any desired viscosity.

Among the special advantages of our invention the following may be mentioned:

1. As there is no interdiffusion of the top coat enamel and the undercoat the latter is sleekproof and there is no temporary loss of tautness and no sinking on subsequent application of the enamel. This permits the production of a complete finish with less coats than heretofore to produce a given build.

2. The system produces a smoother surface than is ordinarily secured at present without resorting to polishing operations.

3. Accelerated tests indicate that the system has a considerably longer life than do other nitrate systems as shown by the superior retention of flexibility when subjected to heat.

4. This clear combination undercoat has the advantage over straight acetate in being cheaper, more moisture resistant and in addition deposits a film over which nitrate top coats give better adhesion.

It will therefore be apparent that we have produced a new aeroplane dope, a new coating system for aeroplane and similar fabrics, and a new method of coating them which gives the desired build and luster without sacrificing durability, and that by suitably changing the pigment or pigments utilized in the lacquer coating it is possible to produce aeroplane fabrics of any desired color or colors without sacrificing any of the desired characteristics of an aeroplane fabric.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments thereof except as defined in the appended patent claims.

We claim:

1. An article of manufacture comprising a taut base sheet of fabric, an undercoat film superposed thereon containing cellulose nitrate and cellulose acetate, and an overcoat film formed by coating over said undercoat film a composition comprising cellulose nitrate and a mixed solvent, the character and proportions of said mixed solvent being such as to have substantially no solvent action on the cellulose acetate in the undercoat film.

2. An article of manufacture comprising a taut base sheet of fabric, an undercoat film superposed thereon containing cellulose nitrate, cellulose acetate, and a common solvent softener therefor, and an overcoat film formed by coating over said undercoat film a composition comprising cellulose nitrate and a mixed solvent, the character and proportions of said mixed solvei being such as to have substantially no solvent action on the cellulose acetate in the undercoat film.

3. An article of manufacture comprising a taut base sheet of fabric, an undercoat film superposed thereon containing cellulose nitrate, cellulose acetate, and a common solvent softener therefor, and an overcoat film formed by coating over said rics, the steps which comprise applying to a taut fabric an undercoat dope comprising cellulose nitrate and cellulose acetate, and applying over said undercoat dope an overcoat composition comprising cellulose nitrate and a mixed solvent, the character and proportions of said mixed solvent being such as to have substantially-no solvent action on the cellulose acetate in the undercoat dope.

GUY C. GIVEN.

HAROLD W. LETTS.

NORMAN W. THOMSON. 

